Keying arrangement



Dec. 24, 1946. E. o. WILLOUGHBY 294l303 I KEYING ARRANGEMENT v FiledOct. 15, 1945 3 Sheets-Sheet l q/2 PASS- Dec. 24, 1946. E. o. WILLOUGHBYKEYING ARRANGEMENT u 5 Sheets-Sheet 2 Filed Oct. l5, 1945 lr/G3.

Dec. 24, 1946. E. o. wlLLoUGHBY 2,4%,013

KEYING ARRANGEMENT Filed 0G13, l5, 1943 'f 5 Sheets-Sheet 3 PatentedDec. 24, 1946 UNITE STAT ES' KEYINGV ARRANGEMENT Application Octoberl,1943,` Serial 4*l\l.0. .506,3 i3 In Great Britain .October ,20.119421 12Claims. (Cl: 2501-11) 4The present invention relates to keying ar-`rangements ior. use with radio frequencies i013 feeding one or other oftwol transmission lines from a circuit, or Vice versa, namely, forfeeding; a circuit alternately from one orother oftWo transmissionlines, and resides in an improvement in or modification of the keyingarrange-- ment described and claimed in United States 4ap-` plication No. 457,797.

In thev parent specication akeyingarrangement of the type specifiedisdescribed which comprisesrejector circuits connected in series intherespective transmission lines and means for altering the capacitiesofthe two rejector circuits simultaneously in such manner that onecapacity movesto-wards the tuning valve Whilst the other moves away fromit. In the embodiment described in the parentgspecication each of therejector circuits Ais formed by a variable capacity connected` across aportion of the line conductor and the capacity being formed by twoconducting plates each connected to a different point on said lineconductor and a third conducting plate in the form of a portion ofcylindrical drum arranged to be brought cyclically opposite the platesso as to form two condensers in seriesto tune or detune the rejectorcircuit to or from the operating frequency. The conducting portions ofthe drum are so arranged that when one rejector circuit is tuned/to theoperating frequency and so allows no current to pass, the capacity ofthe other circuit is great and allows current to pass. InV thisembodiment one of the two series connected condensers of a rejectorcircuit is also included in the other circuit which functions as thepass circuit.

It has been found difficult in practiceY to tune the rejector circuit tothe operating frequency owing to the influence of the pass circuit andthus to obtain an effective block in one transmission linev whilstcurrent passes to the other line.k

The modification according to the present invention comprises a networkin series in each transmission line and means for alternativelybalancing said networks.

The `present invention will be better understood from the followingdescription taken in conjunction with the accompanying drawings inwhich:

Fig. 1 shows the electrical circuit of the arrangements accordingto thepresent invention, assuming the right hand side is in the pass conditionand the left hand side is in the blocking condition;

Fig. 1a is a simplified arrangement of Fig. 1;

Fig.-l 2-is an electrical schematicshcwing conditions of the pass sideof Fig. l;

Fig. 3Y isa-'diagrammatic representation oiA the invention;

Fig.. 41is.an electrical schematic of thearrangement shown in Fig. 3;and

Fig. 5 shows diagrammatically a perspective view of onemechanicalconstruction of the keying arrangement ,according to the presentinvention.

In all thegures, the same references indicate like parts.` v

Referring to Figs. 1 and la the elementary electrical principles andcircuit` evolution of the present invention willrst be described.

InFg. 1a T is a transmission line fro-ma transmitten'and AI and A2 aretransmission lines leadingtothetwo aerials to be. alternatelyF keyed.,

If the capacity CI is made zero the path of the transmission. line A!would be blocked, and if at theusame timethe capacity C3 is present onthe righthandrside of the circuit some power would pass toY thetransmission line A2. Further if C3 is made a suiciently largecapacitythen by the use of Vrnatcliing,stubs between T andearth andA2jand, earth,. itis possible' to match the characteristic'irnpedanceofthe transmission lineT to that of A2 at A2 vand thereby ensure full passof power.

By arranging tovary the capacities ,CI and C3 alternately fromZerototheir pass values, and by the use of ,matching stubs from Al, T,and A2 to earth, full p ower will pass to V,one aerial transmis' signline ,whilethe `other isblocked, andvice versa.

In practice the capacityon the blocked Vsideof the arrangement cannot bemade Zero; hence (referring: to Fig. l) according to the invention abridge @circuit is Lformedloy connecting adjustable capacii-i'esjCgl Cbetween AYI and T and Tand AZ, so thai-, the points IA! and A72 lcan beadjusted to beat-earth potential' during their respectiveblockingperiods. If theginductancebetween D and E isreplaced byacapacitythen C, C mustbe inductancesbutthe vformer arrangement is much to` bepreferred as full. power can be passed with smaller valuesof; thepassvalue of the capacity` Cjl or C3,i. e. vnarrower pole pieces in themechanicall constructionr tobe described hereinafter thereby ypermittinga. quicker changeover between dash'and dot periods.

Fbrtunately,.C| and C31v :areso-srnall in th blocking condition that the.bridge circuit on7 the blocked side of the arrangementis ofvery highimpedance, andthe adjustment of .the block i,l e. of the capacities Cand C is non-critical. The pass condition of the arrangement is ybeststudied fromFig. v2,gWhi-ch isa reearrangement of Fig, 1

and iseacorrect .indication of` the'pass condition' aciaoi 3 when theblock circuit has been Atuned to th-e operating frequency.

The T-network, TD A2E of Fig. 2, can be transformer to a 1rnetwork theseries arm of which when taken in parallel with C' must be of reactanceless than \/Z|Z2, where ZI is the characteristic impedance `of thetransmitter line T and Z2 the impedance characteristic of the aerialfeeder A2. The reactance of the equivalent shunt legs to ear-th isadjusted by stubs connected at D and A2 for matching.

Referring now to Figs. 3 and 4, the practical circuit arrangementbecomes evident, the line T lthe disc D2, and .the transmission lines tothe Y two aerials AI and A2 are connected to the pole pieces Pl and P3,which form condensers Cl and C3 with the sector discs DI and D3respectively.

The centre disc D2 is complete, and the outer discs Dl and D3 are of 90and 270 segments corresponding to the dot and dash periods respectively,eiected by rotation of the discs which are secured in relative positionson a common axle S.

CI, C2 and C3 are the capacities between the rotor and the pole pieces,C2 having a large constant value and Cl and C3 each changed suddenly,the one being a substantially constant pass capacity While ythe other isa substantially constant small blocking capacity.

The tuning for the blocking condition is carried out by the two-Wirestubs TI2 and T23 forming capacities C and C (Fig. 1) and the matchingis effected by the three stubs MI, M2 and M3, connected at the junctionAl, Tl and A'Z respectively, the blocking condition being arranged tooccur when the capacity of the outer pole piece PI or P3 to itscorresponding segment DI or D3 is a minimum, said -capacity being a verysmall stray capacity.

Although adjustable short circuited two-Wire stubs TI2 and T23, nearly90"V in length, are satisfactory for capacities C and C', the linesthemselves should be kept appreciably longer than this (almost 180)otherwise they will, at the same time, represent a very low shunt stubto earth across the pole pieces PI, P2 and P2, P3. Note that it is notpossible to replace the stubs TI2 and T23 by small variable capacitiesas the stray capacities between the pole pieces themselves exceed thoserequired in the blocking circuit, and hence TI2 and T23 are inductive.

The capacity C2, i. e. between P2 and D2 is arranged to be very large byusing a large pole piece P2 and inductance is obtained between the shaftS and casing K by the use of re-entrant .tubes KI K2 to carry thebearings, the shaft and casing forming a short-circuited transmissionline whose positive reactance swamps the capacitative reactance betweenthe rotor S, DI, D2

and D3 and casing K. The capacity 'Cl or C3,l

i. e. between DI and PI, and between D3 and P3, is made as small as isconsistent with full pass of power as this enables a quick changeoverfrom dash to dot period or vice versa to be obtained.

The preceding paragraph shows that the setting of the blockingconditions are independent of the line matching conditions and thismakes the keying arrangement Very simple .to adjust,

provided the operations are carried out in th correct sequence.

All that is required is an indicating system adjacent to each of theaerials, the feeders of which are AI and A2. At first the block on .the

4 lef-t hand side is adjusted and the rotor is turned so that thecapacity between Pl and DI is a minimum. The stub TI2 is then adjustedso that no sign-al is picked up from the aerial Al.

Then, turning the rotor, a similar operation is carried out with T23 fora block on the opposite side of the circuit, at the same time adjustingthe matching stubs MI and M2 .to give maximum transfer of power 4to theaerial Al. The rotor is then turned until AI is again blocked and thestub-M3 adjusted until maximum power is transferred on the aerial A2.

The keying arrangement is now completely adjusted.

The mechanical assembly is shown in Fig. 5 in whichl the pole pieces PI,P2, P3 are shown as members or hoods having cross sections of invertedU-shape between which the sectors or discs DI, D2, D3 pass. D2 is acomplete disc and DI and D3 are sectors complementary one to the otherso that together they occupy a complete disc and 'are so -arranged onthe shaft S that when DI is under its hood PI, the gap in D3 is oppositethe hood P3. The hoods PI and P3 have the same lengths circumferentiallyof the sectors DI and D3 to form therewith approximately equalcapacities, but the hood P2 is made substantially longer than Pl or P3in order to form a larger capacity with D2 than do Pl and P3 with DI andD3 respectively. The hoods are of course insulated from the outer casingK.

The shaft S is extended outside of the casing K and provided at each endwith tubular casings Kl, K2, so as to for-m therewith portions ofcoaxial line. The casings Kl and K2 are electrically connected to themain casing K. Short circuiting discs LI, L2 are provided slidablymounted on the shaft. These discs are provided with manipulating devicesin the form of small flat plates HI, H2 which protrude through an axialslit provided in the members KI and K2, so that the discs can beadjusted along the coaxial lines. The shaft S is further provided at oneend with a Wheel W, which is preferably a toothed wheel, by which theshaft S may be coupled to a motor or other device for rotating the discsDI, D2, D3.

The tuning stubs TI2 and T23 comprises twowire lines enclosed in outercasings K3 and K4, respectively, electrically connected to the maincasing K. The lines TI2 and T23 are provided with short circuiting orbridging members BI, B2 which are slidable along their respective lines.

The matching stubs Ml, M2, M3 comprise lengths of coaxial conductorlines the outer conductors of which are cut away in the vicinity of thehoods PI, P2 and P3 to enable the inner conductors to be connected tothe respective hoods. The outer conductors are electrically connected tothe outer casing K. The lines Ml M2 and M3 are each provided with shortcircuiting devices which are adjustably movable by means of themanipulating plates H3, H4 and H5 which project through axial slitsprovided in the outer conductor for the purpose. Y

In operation, the shaft S is rotated and the disc DI when under the hoodPI unbalances the bridge as hereinbefore described and current passes toA! whilst the gap in D3 is opposite its associated hood and the bridgeon that side of the arrangement is balanced, thus forming a block to theoperating frequency and no current passes to A2..

When D3 is under its hood P3, the bridge circuit to A2 is unbalancedWhilst the circuit to Al is blocked, so that the aerials AI and A2 arefed in a dot-dash rhythm.

Y Whilst nofparticular bearings have. beenshown inthe drawings fortheshaft S,.the;discsK-l `tand KET may be adapted Jas such. In'thiscasethe bearings have to serve two purposes, namely (a) They have towithstand a speed which may be of the order of 30G-400 revolutions perminute continuous service (24 hours per day).

(b) They have to provide an electrical return circuit for the currentsbetween the rotor and the casing K.

Hence, although ball bearings have been used with reasonablesatisfaction Oilite bearings, which are a variety of sleeve bearingcapable of continuous service, are the best compromise between theelectrical and mechanical requirements.

Whilst one embodiment of the invention has been described by way ofexample, others falling within the scope of the appended claims willoccur to those skilled in the art.

It will be understood that the keying arrangement according to thepresent invention may be Y used in any case where the arrangementdescribed and claimed in the parent specification can be used. Forexample, the arrangement may be used as the keying arrangements in ablind approach system for aircraft orfor alternately blocking twoalternative paths differing in length so as to introduce a phasediierence in the current traversing one path with respect to the other,as described in the parent specification. The keying arrangementaccording to the invention may also be used with radio receivers, forexample in known type of homing arrangements for aircraft in which theaircraft carries two antenna systems having overlapping characteristicdistribution diagrams, the said antenna systems being arranged to feedalternatively into a receiver circuit. In such cases the homing iseffected on a single transmission beacon on the ground and dot-dashsignals are produced by the keying arrangement in the receiver, the pathto be followed by the aircraft being defined by dot and dash signals ofequal or constant ratio signal levels.

Other embodiments and applications of the invention falling within thescope as dened in the apended claims -will occur to those skilled in theart.

What is claimed is:

1. A keying arrangement for use with radio frequencies for connectingone or the other of two transmission lines to a circuit, comprising anetwork in series in each transmission line and means for alternativelybalancing said networks.

2. A keying arrangement as claimed in claim 1 wherein said networks eachcomprises a variable capacity connected across a portion of thetransmission line conductor and means for varying the capacities so asalternately to balance and unbalance said networks.

3. A keying arrangement for use with radio frequencies for connectingone or the other of two branch transmission lines to a main transmissionline comprising means to connect said two branch transmission lines to apoint on said main transmission line, a network connected in series ineach branch transmission line and comprising a variable capacityconnected across a portion of each branch transmission line, saidvariable capacity consisting of a fixed capacity in series with avariable capacity, and means for alternatively balancing said networksby adjusting said variable capacities.

`having a stationary member and a conductive element movable into andout of capacity relationship therewith, said variable capacity of eachnetwork including as a part thereof, common to both networks, a fixedcapacity havin-g two relatively movable conductive members capable ofrelative movement without changing the xed capacity therebetween andmeans for alternatively balancing said networks by adjusting saidvariable capacities. l

6. A keying arrangement as claimed in claim 5 in which said disc andsectors are secured to the same shaft so as to be rotatable together. v7. A keying arrangement as claimed in claim 5 in which said rotatabledisc and sectors are secured to the same shaft so as to be rotatabletogether, andrsin which an earthed screen is provided and sa'idrotatable disc and sectors and stationary members, together with theportions of the transmission line across which the capacities betweensaid discs and sectors and their respective stationary members areconnected, are enclosed within said eartlied screen and together withthe line and the capacities formed by said fixed members sectors anddisc, the branch lines, and said screen form a T-network.

8. A keying arrangement for use with radio frequencies for connectingone or the other of two branch transmission lines to a main transmissionline, comprising means to connect said two branch transmission lines toa point on said main transmission line, a network in series with each ofsaid branch transmission lines, a single shaft for controlling thebalancing and unbalancing of said networks, each of said networkscomprising a Variable capacity having a sector of a disc mounted on saidshaft, and a stationary member forming a capacity with said sector, saidvariable capacity of each network including as a part thereof, common toboth networks, a single fixed capacity having a rotatable disc alsomounted on said shaft and a stationary member forming a capacity withsaid disc, and means for alternatively balancing said networks byadjusting said variable capacities, tuning stubs provided in both branchtransmission lines, and matching stubs, one being provided at thejunctures of each branch transmission line and its associated networkand one at said point on said main transmission line.

9. A keying arrangement as claimed in claim 5 in which said disclsectors are complementary one to the other and are arranged to beopposite their respective stationary members at diiferent times.

10. Akeying arrangement as claimed in claim 1 incorporated in a radiosystem comprising two antennae or antenna systems alternately energisedfor defining an approach path for aeroplanes, ships or other vehicles.

11 A keying arrangement as claimed in claim 1 incorporated in a homingsystem for aircraft,

homing on a single transmission beacon, in which the aircraft isprovided with tW'o' antennae or .12. A keying arrangement as claimed inclaim antenna systems having overlapping character- 1 incorporated in a.transmission system for alistic distribution diagrams and a receiver,said ternately blocking two alternative paths differing arrangementbeing incorporated in said receiver in length so as to introduce a phasedifference for alternatively feeding to the receiver in a dot- 5 in thecurrent traversing one path with respect dash rhythm the/waves picked upby said antothe other.

tennae or antenna systems. ERIC OSBORNE WILLOUGHBY.

